The present invention relates generally to a technique for delivering high pressure fluids to a downhole location, and particularly to a technique for balancing the pressures acting on a downhole disconnect.
Downhole tools for use in a variety of wellbore applications are often connected to a tubing string, such as a coiled tubing string. The tubing may be connected to a tool or tools by a disconnect that permits disconnection of the tool if, for example, the tool becomes stuck in the wellbore. By applying a tensile load or other input, the disconnect releases the tool to permit withdrawal of the tubing. Certain mechanical disconnects are calibrated to release at a preset release load upon application of a sufficient tensile load to the tubing.
In an exemplary application, a high pressure fluid, such as a liquid, is delivered to the tool through the tubing. The internal pressure is greater than the external wellbore pressure and this allows use of the high pressure fluid to perform a variety of tasks, such as cracking of the surrounding formation. However, current mechanical disconnects are not pressure balanced. In other words, the differential pressure between the internal pressure and the external, wellbore pressure causes a force tending to separate the disconnect. This is undesirable, because a sufficiently high pressure differential can cause unexpected release of the tubing from the tool or tools without application of the release load to the tubing. If the preset release load is raised to avoid unexpected release, however, the tensile load required to cause a desired release may exceed the tensile limit of the tubing.
The present invention relates generally to a system for facilitating disconnection of a tool at a downhole location. The system comprises a tubing and a tool. Additionally, a mechanical disconnect is positioned between the tubing and the tool to permit release of the tool from at least a portion of the tubing. The mechanical disconnect is pressure compensated to ensure release of the tool only upon application of the predetermined tensile load to the tubing.
According to another aspect of the present invention, a mechanical disconnect is provided for use in a downhole environment. The mechanical disconnect includes an upper portion and a lower portion. A shear member is connected between the upper portion and the lower portion. Also, a pressure balance system is utilized. The pressure balance system includes pressure areas exposed to a relatively high internal pressure to balance the axial forces acting on the lower portion.
According to another aspect of the present invention, a method is provided for supplying a fluid under relatively high pressure to a tool disposed downhole in a wellbore. The method comprises pressurizing the fluid in a tubing disposed in a wellbore. The method further comprises directing the fluid through a mechanical disconnect to the tool. Additionally, the method includes pressure balancing the mechanical disconnect to provide counteracting axial forces.